Generally, a lens module includes a lens barrel, lenses received in the lens barrel, and a set collar secured to the lens barrel by an adhesive for holding the lenses in the lens barrel. The lens barrel comprises a stepped inner wall for supporting the lenses thereon. Each lens comprises a central optical portion and a circumferential locating portion with lower and outer surfaces thereof engaging with the stepped inner wall of the lens barrel. The set collar is configured as an annular ring corresponding to the locating portion of the uppermost lens and holds the uppermost lens in the lens barrel. The set collar also defines a central opening which is aligned with the optical portions of the lenses when the set collar is placed on the uppermost lens. An outer surface of the annular portion of the set collar abuts closely against the stepped inner wall of the lens barrel to isolate the lenses from an exterior of the lens barrel. The set collar forms an annular flange surrounding a central opening defined in the set collar. A space defined between the flange and the lens barrel is filled with the adhesive to fix the set collar to the lens barrel, and thus the lenses are held in the lens barrel.
In the case mentioned above, the lenses cannot be adjusted relative to the lens barrel, once the set collar is placed into the lens barrel. Therefore, before the set collar is placed into the lens barrel, the lenses must already be accurately positioned. However, the lenses, especially the uppermost lens, are prone to shifting during assembly of the set collar into the lens barrel. This shifting of the lenses cannot be adjusted unless the set collar is removed from the lens barrel. In addition, because the outer surface of the annular portion of the set collar abuts closely against the stepped inner wall of the lens barrel, the adhesive is merely applied between the set collar and the lens barrel, and the reliability of the lens module is low.
Therefore, what is desired is a lens module with high reliability and precise positioning of lenses therein.